1. Field of the Invention
The present invention relates to a multilayered piezoelectric element in which a plurality of piezoelectric ceramic layers and a plurality of electrode formation layers are alternately laminated. The present invention also relates to a method of producing the multilayered piezoelectric element.
2. Description of the Related Art
A multilayered piezoelectric element is comprised of piezoelectric ceramic layers and electrode formation layers that are alternately laminated, The piezoelectric ceramic layer is deformable, expanded and/or contracted when a voltage is applied. The electric forming layer forms an internal electrode. For example, Japanese patent laid open publication No. JP 2007-258280 has disclosed a conventional multilayered piezoelectric element. In the production of such a multilayered piezoelectric element, a electrode material containing AgPd alloy is printed on a green sheet made of multilayered piezoelectric ceramic, and a plurality of those printed green sheets is laminated in a lamination direction, and the green sheets forming a lamination are integrally fired.
A recent demand in this technical field is to improve or increase the deformation dimension of such a multilayered piezoelectric element when a voltage is applied. In order to solve such a recent demand, various types of piezoelectric materials have been developed. In particular, according to environmental conservation and for reducing influence to the environment, it is strongly demanded to develop a piezoelectric material of lead free material which does not contain any lead. For example, Japanese patent laid open publications No. JP 2002-68835, JP 2002-68836, JP2004-244299, JP2004-323325, and JP2006-56778 have disclosed such lead free piezoelectric materials containing no lead.
However, because such conventional lead free piezoelectric materials have low piezoelectric characteristics, a multilayered piezoelectric element made of those lead free piezoelectric materials cannot provide a necessary deformation dimension.
In order to solve such a conventional problem in the piezoelectric material filed, for example, Japanese patent laid open publication No. JP 2006-28001 has disclosed a crystal-oriented ceramics made of polycrystalline material that is made mainly of isotropic perovskite type compound. In the crystal-oriented ceramics, crystals are oriented in a specific direction (or a specific crystal plane). Because this crystal-oriented ceramics has a high density and a highly crystal orientation, it is expected to improve or increase the deformation properties of the multilayered piezoelectric element comprised of the crystal-oriented ceramics as piezoelectric ceramic layers.
However, when the multilayered piezoelectric element comprised of piezoelectric ceramic layers and electrode formation layers that are alternately and integrally laminated is produced using such crystal-oriented ceramics made of polycrystalline material that is made mainly of isotropic perovskite type compound, a component element such as Ag forming the inner electrode is easily evaporated, or diffused into the ceramics. As a result, this decreases the electrode formation ratio of an electrode part to the total surface of the electrode formation layer.